Gaseous discharge display device

ABSTRACT

The specification describes a flat panel gaseous discharge display device in which the display illumination is formed at least in part by luminescence resulting from excitation of an appropriate phosphor by low energy electrons drawn from a glow discharge. To provide scan, the discharge is either itself moving in stepwise fashion between discrete cells or is a secondary discharge primed by a scanning discharge and triggered by the display information signal. Varying the current through the phosphor produces gray scale. Illumination from the gaseous discharge may be mixed with the phosphor for color balance and increased brightness. The phosphor can be divided into color stripes with means for selective energization of the stripes to form a color display.

United States Patent 1 1 Chen et al. 451 N 6, 1973 GASEOUS DISCHARGEDISPLAY DEVICE 3,648,093 3/1972 Kupsky 313/217 3,654,508 4/1972 Caras 751 Inventors. 3,701,917 10 1972 Kupsky 313/188 9 1 lrv'nGd C ttt'- I):l gg g gzz g f g gg j Primary Examiner-W1ll1am F. Lmdqu1st Howard Rowen,Florham Park, all of Atmmey w' Keefauver ct NJ.

[73] Assignee: Bell Telephone Laboratories, [57] ABSTRACT Incorporated,Berkeley Heights, NJ. The specification describes a flat panel gaseousdis- [22] Filed, Nov 9 1972 charge display device in which the displayillumination is formed at least in part by luminescence resulting [21]Appl. No.: 305,188 from excitation of an appropriate phosphor by lowenergy electrons drawn from a glow discharge. To pro- [52] U S C]313/218 313/109 5 313/188 vide scan, the discharge is either itselfmoving in step- 313/217 wise fashion between discrete cells or is asecondary 51] In! H01 17/04 61/06 discharge primed by a scanningdischarge and triggered [58] Fieid 3J13/1095 217 by the displayinformation signal. Varying the current 5 through the phosphor producesgray scale. Illumination from the gaseous discharge may be mixed withthe 56 phosphor for color balance and increased brightness. I 1 g izCited The phosphor can be divided into color stripes w1th ST TBS PATENTSmeans for selective energization of the stripes to form 3,508,|01 4/1970Tanji 313/1095 a color la 3,509,402 4/1970 Du Bois, Jr. et al. p y3,559,190 1/1971 Bitzer et al. 3l3/l09.5 X 14 Claims, 6 Drawing FiguresPATENTEDNUY SL973 W 3.771.008

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' SHEET w 3 PATENTEDRBY s 1913 SHEET 3C? 3 FIG. 5B

FIG.5A

O fio l GASEOUS DISCHARGE DISPLAY DEVICE This specification describes aflat panel realtime display system based on the excitation of lowvoltage phosphors by low energy electrons drawn from a gaseousdischarge. The discharge may beitself moving in stepwise fashion betweendiscrete discharge cells or can be a secondary discharge selectivelyprimed. by a moving discharge. The chief advantages of the device arethat it provides in a relatively straightforward manner full gray scalecoupled with low voltage addressing and the option of full colordisplay. Such a combination of features is not available in any flatpanel display device known to date.

BACKGROUND OF THE INVENTION To understand the operation of this device,it is useful to first describe some approaches to flat panel displayreported in recent prior art.

A gas discharge device in which the discharge is localized and caused toscan through an array of discharge cells in a rasterlike fashion is theobject of extensive development for a variety of flat panel displayapplications. Various aspects of this device aredescribed in The PrimedGas Discharge Cell A Cost and Capability Improvement for Gas DischargeMatrix Displays, I970 IDEA Symposium, Digest of Papers, pp. 30-31, May1970, by G. E. Holz. A similar idea is described by H. Hori, K. Kasaharaand K. Inoue, A. New Gas-Discharge Display Device Using Through- HoleEnhancement, 1970 IEEE Conference on Display Devices, New York, DecemberI970. In this device, light is generated by the negative glow in a gasand m scan anodes may be moved by connecting to a a common bus bar everypth cathode and driving the cathodes with a p-phase clock. Informationis displayed along a line defined by a given cathode conductor bystriking a discharge in the display cells using signals applied to thedisplay anodes. Since the display cell is primed by diffusion ofmetastable ions from the scan region, the voltage required is somewhatless than the full striking voltage. This gas discharge scan system thuseliminates almost one-half of the leads and switches necessary for aconventional matrix-addressed system.

Multicolor displays have been produced by coating the walls of eachdisplay cell with a phosphor and. exciting the phosphor with the uvemission of the discharge. The cell covers are made translucent ratherthan transparent to diffuse the colors. The saturation property of thephosphor is exploited to produce a range of colors: at low current, thephosphor emission dominates; at high current levels, the red glow,characteristic of the neon discharge, is seen. This approach to flatpanel color display is described in "Plasma Display Changes Color asCurrent Input Changes", Electronics, pp. 44, 66, July 1971, by R. A.Cola. One drawback to this device is the lack of independent control ofcolor and intensity when more than one color is desired.

Another prior art gas discharge display device, reported by Kazan andPennebaker in Proceedings of IEEE, Vol. 59, pp. 1130-1131, July 1971,consists of a cylindrical glass envelope, filled with about 5 torr ofHe, and containing a strip cathode and a strip anode spaced to form agas discharge. Spaced beyond the anode is a third electrode, the displayanode, coated with a zinc oxide phosphor and with means for varying itspotential with respect to the anode. A glow discharge, maintainedbetween the cathode and primary anode, creates above the display anode aplasma from which electrons may be withdrawn to excite the phosphor.Under DC excitation, a brightness of about IL .at a phosphor voltage of10 volts with respect to the primary anode and current density of about1.2 mA/cm has been reported. A practical device can be made by breakingup the display anode into a number of individually addressed segments.The important feature of this device is the substitution of a plasmacathode for the thermionic cathode used in several commercial devicesemploying anodes coated with low voltage phosphors. The virtue of thisapproach is that it provides low voltage addressing and a cathode whichmay be used in uniformly exciting an area several inches in eachdimension. The chief drawbacks of the scheme, when applied to large areadisplays, are that it does not lend itself to matrix addressing and thatthe maintenance of an extended glow discharge to generate the plasmawhile exciting only localized segments (as in a timeshared application)is not efficient.

BRIEF STATEMENT OF THE INVENTION The device according to the inventionavoids in large measure the drawbacks of the prior art devices whiletaking advantage of their virtues. It is characterized by a stepped gasdischarge to provide the scanning function, and an array of displayanodes which either selec- DETAILED DESCRIPTION OF THE INVENTION In thedrawing:

FIG. 1 is an exploded schematic view of one embodiment of a flat paneldisplay device incorporating the advantageous features of the invention;

FIG. 2 is a sectional view of the panel of FIG. 1;

FIG. 3 is a view similar to that of FIG. 1, showing an alternativeembodiment;

FIG. 4 is a schematic cross section of the device of FIG. 3, showing theselective generation of the second discharge as a source of electronsfor the low voltage phosphor; and

FIGS. 5A and 5B are schematic representations of discharge cellsillustrating an alternative form of display anode useful with either ofthe devices previously described.

The display device of FIG. 1 includes a front glass cover 10 which inthis configuration functions as a support substrate for the displayanodes 11. The display anodes are addressed through leads 12. Thedisplay anodes comprise a transparent electrode strip coated with a lowvoltage phosphor. Effective operation has been demonstrated with adisplay anode consisting of indium-tin oxide stripesphotolithographically applied to the glass cover and coated with Pphosphor (3.5 mg/cm). A phosphor with sufficient lateral conductivitycan be used alone.

Referring again to FIG. 1, the display anodes are shown as stripes intrios 13, 14, 15, an exemplary arrangement for color display. Eachstripe of a trio consists of a different color phosphor, known in theart of color video display, with electrical addressing means independentof the other stripes in the group. Color selection is made byelectrically addressing common colored phosphor stripes via one or moregroups of leads 16, l7, 18.

The glass cover 10, carrying the display anodes, is made part of theconventional gas discharge panel comprising an insulating spacer 19,with an array of cavities 20, and the scanning assembly, which basicallyincludes crossed electrode grids 21 and 22 and insulating spacer 23. Inthis configuration, the electrode stripes of the scan anode grid 21extend in the row direction and are addressed by row address leads 27.The electrodes of the cathode grid 22 extend in the column direction andare addressed by column address leads 28. The display anode stripes arearranged parallel to the row scan anodes, the direction of scan. Thestepped discharge is controlled by stepping the cathode grid whichtherefore is orthogonal to the scan direction and to both anode grids.

The scanning assembly defines a matrix of gas discharge cells thatcreate a reservoir plasma from which electrons can be selectivelyextracted to provide localized illumination for a given picture element.The electrons are extracted through apertures 24 in the scan anode grid21 when the appropriate display anode lead 12 is energized.

The cathode scanning grid 22 is shown deposited on the rear panel cover25. The anode grid 21 can be a self-standing conductive grid, or cancomprise a conductor array deposited or formed on a support sheet.

The panel of FIG. 1 is shown assembled and in cross section in FIG. 2.

Various structures for the discharge cells and the scanning electrodesare known, some of which are described in the prior art alluded toabove. Other description can be found in U. S. Pat. No. 3,617,796,issued Nov. 2, 1971; U. S. Pat. No. 3,619,700, issued Nov. 9, 1971; U.S. Pat. No. 3,626,235, issued Dec. 7, 1971; U. S. Pat. No. 3,626,244,issued Dec. 7, 1971; U. S. Pat. No. 3,648,093, issued Mar. 7,1972; andU.S. Pat. No. 3,654,508, issued Apr. 4, 1972.

For example, an alternative embodiment in which at least a part of thevisible display is produced by excitation of low voltage phosphors butin which the electrons are selectively extracted in a somewhat differentway is shown in FIG. 3. The important structural distinction in thisdevice is that the cathode and scan anode grids are interchanged. Thefront glass cover 30, rear glass cover 31, display anode grid 32,cathode grid 33 with openings 34, scan anode grid 35, and aperturedinsulating spacer 36, separating the display anodes from the upper scanelectrode grid are substantially constructed as in the device of FIGS. 1and 2. The insulating spacer means separating the scan discharge gridscan be made integral with the rear glass cover 31, as shown.

Whereas this embodiment is similar structurally to the formerembodiment, certain differences will be evident from the partlyschematic sectional view of FIG. 4. The gas discharge steps alongbetween the scan anode 35 and the cathode grid formed by electrodestripes 33. The openings 34 allow metastable ions to diffuse through thecathode grid into the secondary discharge cells formed in the spacer 36.These metastable ions prime each of the secondary cells in a mannerknown in the art to trigger the secondary discharge between the cathodesand display anodes 32. The secondary discharge is selective, shown hereby activated electrode 32a and unbiased electrode 32b. The improvementaccording to the invention is the provision of a low voltage phosphor 37as, or in combination with, the display anode grid. Electrons producedby the secondary discharge are selectively attracted to the displayanode and activate the phosphor.

The structure of the display anode can be modified to advantage byaperturing the anode, insulating the underside and causing the electronsto activate the upper surface of the phosphor layer as shown in FIGS. 5Aand 58. FIG. 5A is a schematic representation of the discharge cell ofthe device of FIGS. 1 and 2, while FIG. SBschematically illustrates asimilar phosphor activation scheme for the discharge device of FIG. 4.The device with this inverted display anode configuration is constructedand operated essentially as before. The important structuralmodifications are the provisions of apertures 50 in the scan anodes andan insulating layer 51 so that the electrons impinge on the far side ofthe anode. the insulating layer may be any of a variety of knownmaterials. Glass or alumina is appropriate.

The virtue of this arrangement is that the electrons drawn from thedischarge will strike the surface of the phosphor facing the viewer asshown, rather than the inner surface, and the light generated (mostly atthe surface of the phosphor layer) will not suffer attenuation due totransmission through the phosphor layer.

To demonstrate the efficacy of the novel form of display anode thatforms the basis for the invention, a matrix of gas discharge cellsdriven by 7 anodes and cathodes was assembled in the form shown in FIG.3. The display anodes consisted of the glass cover coated withtransparent electrode stripes, with a phosphor layer over the electrodestripes. The electrode stripes were made by sputtering indium-tin oxideover the glass cover, defining the stripe pattern with aphotolithographic mask and etching with 50% I-lCl at 50 C for 5 minutes.The phosphor was P 15, settled onto the electroded cover plate from adistilled water suspension. The faceplate was sealed into a panel withthe scanning assembly shown, pumped out to about 4 X 10 torr and filledwith neon at 95 torr (pd 9.5 torrcm) in one instance and with neon at 95torr and argon at 0.5 torr (Penning mixture) in another.

To establish the scan function, V were applied to the scan anodesthrough 160 K ohm resistors and the cathodes were switched between V and80 V, representing respectively the on and the off states. The cathodearray was energized with a three-phase drive, with a clock frequencyheld at 8 kHz, and the reset pulse for the reset cathode was maintainedat 200 microseconds in length, with a period of 12.5 milliseconds. Thus,each row was active for 125 microseconds at a time, with a duty cycle ofU100. The display anodes were directly connected to the collector of a2N5282 PNP transistor in the grounded emitter configuration. Theintensity of the glow of the cells was controlled by changing the basecurrent.

the P phosphor, balance this with the illumination 10 from the glow,discharge, and obtain a black and white display. To do this requires thephosphor to cover the glow discharge region. Other utilizations of thelow energy electron excitation mechanism require blanking of the glow togive a pure luminescent output. For example, blanking the glow isdesirable for color display. Blanking the glow to the exterior of thedevice can be achieved in a variety of ways. The cathode can begeometrically shaped with respect to the aperture so no glow is visible,or an electrically inert spacer can be provided over the otherwisevisible region of the glow. The latter expedient is illustrated inFIG.5A, wherein a glass or ceramic spacer S Sis show n blanking the glowthat would otherwise be visible from the front panel. This invention isdirected to both types of embodiments. Alternatively, a gas with lowluminosity, e.g., xenon, can be used, making a blanking structureunnecessary, or the apertures can be offset to achieve the same result.

The performance of the device just described established that anappealing black and white display can be obtained with the displayoperated in a line-at-a-time video mode having a line time of 125microseconds and frame time of 1/30 seconds to give an average cellbrightness of fL at 0.5 A/cm Color display devices, using phosphorsincorporated into gas discharge panels, like that of FIG. 1, arereasonably straightforward extensions in principle and performance.

The phosphors useful in the devices described are those capable ofexcitation by low voltage electrons. Phosphors that are excited bydirect injection of free electrons from space are normally termedcathodoluminescent phosphors. However, because of the origin of thisterm, there is a tendency to construe its meaning in connection withelectrons produced in a conventional cathode ray tube. Typically, theseelectrons are high voltage electrons. For the purposes of defining thisinvention, the appropriate phoshors will be termed low voltagecathodoluminescent phosphors. In turn, low voltage is intended to meanvoltages not exceeding 100 volts.

Various additional modifications and extensions of this invention willbecome apparent to those skilled in the art. All such variations anddeviations which basically rely on the teachings through which thisinvention has advanced the art are properly considered to be within thespirit and scope of this invention.

What is claimed is: t

l. A gaseous discharge flat panel display device comprising:

a gas-tight, panel-shaped gas-filled envelope having an insulatingbottom plate and an insulating top plate, and disposed therebetween afirst parallel grid of electrode elements;

a second parallel grid of electrode elements extending orthogonal tosaid first grid;

insulating spacing means between the first and second grids, saidspacing means being apertured, leaving cavities extending betweenportions of said first and second grids with one aperture for each lineof one of the parallel grids to form an array of discharge cells, eachcell corresponding to the area of the vertical intersection of theelectrode elements of the first andsecondarray; insulating spacing meansoverlying said second grid, having apertures therethrough correspondingto each discharge cell and defining a multiplicity of display cavities,each communicating with a dishar e s llthrwsh, t s 0'29 evenin s. anarray of display anodes disposed between the dis play cavities and thetop plate and extending parallel to one of said first and second grids;

the invention characterized in that the display anodes compriseconductive low voltage cathodoluminescent phosphor elements.

2. The device of claim 1 in which the conductive phosphor elementscomprise conductive stripes coated with low voltage cathodoluminescentphosphor.

3. The device of claim 2 in which some conductive stripes are coatedwith one color phosphor and others with another color phosphor.

4. The device of claim 2 in which every third conductive stripe iscoated with one color phosphor and every group of third stripes iscoated with a different color phosphor.

5. The device of claim 2 in which the conductive stripes are indium-tinoxide and the low voltage cathodoluminescent phosphor is P 15 phosphor.

6. The display device of claim I having additionally an insulating blankcovering one or more of the openings in the electrode grid elements toprevent illumination from the glow discharge from strking the top plate.

7. A gaseous discharge flat panel display device com prising:

a gas-tight, panel-shaped gas-filled envelope having an insulatingbottom plate and an insulating top plate,

a cathode grid of parallel electrode elements supported by the bottomplate,

an insulating slotted spacer overlying the cathode grid, with the slotsextending orthogonal to the cathode grid electrode elements,

a scan anode grid of parallel electrode elements overlying theinsulating spacer with the electrode elements aligned with andsubstantially covering the slots in the spacer, the electrode elementsfurther having openings through their thickness with at least oneopening approximately vertically aligned with an electrode element ofthe cathode grid below,

an apertured spacer overlying the scan anode grid having a row array ofapertures each aligned with the vertical intersection of one of thecathode and scan anode electrode elements and communicating with theslotted portions of the insulating slotted spacer through at least oneof the openings in the scan anode grid,

and a display anode grid overlying the apertured spacer, the displayanode grid having parallel display anode elements with each elementaligned with a row of apertures in the apertured spacer and with a scananode electrode element, the display anode elements further comprising alow voltage cathodoluminescent phosphor.

8. The display device of claim 7 in which the display anode elements aresupported by the insulating top plate.

9. The display device of claim 7 in which the display anode gridelements are coated on the side facing the aperture array with aninsulating material and further have at least one opening through theregion of their thickness corresponding with each aperture to allowelectrons drawn from the aperture to strike the side of the displayanode elements that faces the insulating top plate.

10. A gaseous discharge flat panel display device comprising:

a gas-tight, panel-shaped, gasfilled envelope having an insulatingbottom plate and an insulating top plate,

a scan anode grid of parallel electrode elements supported by the bottomplate,

insulating spacing means extending between the elements of the scananode grid,

a cathode grid of parallel electrode elements overlying the spacingmeans with the electrode elements extending orthogonal to the elementsof the scan anode grid, and having openings through their thickness withat least one opening approximately vertically aligned with an electrodeelement of the anode grid below,

an apertured spacer overlying the cathode grid having a row array ofapertures each aligned with the vertical intersection of one of the scananode and cathode elements and communicating with the cathode gridelectrode elements through at least one of the openings in the cathodegrid,

and a display anode grid overlying the apertured spacer, the displayanode grid having parallel display anode elements with each elementaligned with a row of apertures in the apertured spacer and with a scananode electrode element, the display anodes further comprising a lowvoltage cathodoluminescent phosphor.

11. The display device of claim 10 in which the low voltagecathodoluminescent phosphor is Pl 5 phosphor and the gas comprises neon.

12. The display device of claim 10 in which the display anode gridelements are coated on the side facing the aperture array with aninsulating material and further have at least one opening through theregion of their thickness corresponding with each aperture to allowelectrons drawn from the aperture to strike the side of the displayanode elements that faces the insulating top plate.

13. The display device of claim 10 in which the gas comprises neon.

14. The display device of claim 10 in which the gas comprises xenon.

1. A gaseous discharge flat panel display device comprising: agas-tight, panel-shaped gas-filled envelope having an insulating bottomplate and an insulating top plate, and disposed therebetween a firstparallel grid of electrode elements; a second parallel grid of electrodeelements extending orthogonal to said first grid; insulating spacingmeans between the first and second grids, said spacing means beingapertured, leaving cavities extending between portions of said first andsecond grids with one aperture for each line of one of the parallelgrids to form an array of discharge cells, each cell corresponding tothe area of the vertical intersection of the electrode elements of thefirst and second array; insulating spacing means overlying said secondgrid, having apertures therethrough corresponding to each discharge celland defining a multiplicity of display cavities, each communicating witha discharge cell through at least one opening; an array of displayanodes disposed between the display cavities and the top plate andextending parallel to one of said first and second grids; the inventioncharacterized in that the display anodes comprise conductive low voltagecathodolumInescent phosphor elements.
 2. The device of claim 1 in whichthe conductive phosphor elements comprise conductive stripes coated withlow voltage cathodoluminescent phosphor.
 3. The device of claim 2 inwhich some conductive stripes are coated with one color phosphor andothers with another color phosphor.
 4. The device of claim 2 in whichevery third conductive stripe is connected to a common electrical lead,every third stripe is coated with one color phosphor and every group ofinterconnected stripes is coated with a different color phosphor.
 5. Thedevice of claim 2 in which the conductive stripes are indium-tin oxideand the low voltage cathodoluminescent phosphor is P 15 phosphor.
 6. Thedisplay device of claim 1 having additionally an insulating blankcovering one or more of the openings in the electrode grid elements toprevent illumination from the glow discharge from strking the top plate.7. A gaseous discharge flat panel display device comprising: agas-tight, panel-shaped gas-filled envelope having an insulating bottomplate and an insulating top plate, a cathode grid of parallel electrodeelements supported by the bottom plate, an insulating slotted spaceroverlying the cathode grid, with the slots extending orthogonal to thecathode grid electrode elements, a scan anode grid of parallel electrodeelements overlying the insulating spacer with the electrode elementsaligned with and substantially covering the slots in the spacer, theelectrode elements further having openings through their thickness withat least one opening approximately vertically aligned with an electrodeelement of the cathode grid below, an apertured spacer overlying thescan anode grid having a row array of apertures each aligned with thevertical intersection of one of the cathode and scan anode electrodeelements and communicating with the slotted portions of the insulatingslotted spacer through at least one of the openings in the scan anodegrid, and a display anode grid overlying the apertured spacer, thedisplay anode grid having parallel display anode elements with eachelement aligned with a row of apertures in the apertured spacer and witha scan anode electrode element, the display anode elements furthercomprising a low voltage cathodoluminescent phosphor.
 8. The displaydevice of claim 7 in which the display anode elements are supported bythe insulating top plate.
 9. The display device of claim 7 in which thedisplay anode grid elements are coated on the side facing the aperturearray with an insulating material and further have at least one openingthrough the region of their thickness corresponding with each apertureto allow electrons drawn from the aperture to strike the side of thedisplay anode elements that faces the insulating top plate.
 10. Agaseous discharge flat panel display device comprising: a gas-tight,panel-shaped, gas-filled envelope having an insulating bottom plate andan insulating top plate, a scan anode grid of parallel electrodeelements supported by the bottom plate, insulating spacing meansextending between the elements of the scan anode grid, a cathode grid ofparallel electrode elements overlying the spacing means with theelectrode elements extending orthogonal to the elements of the scananode grid, and having openings through their thickness with at leastone opening approximately vertically aligned with an electrode elementof the anode grid below, an apertured spacer overlying the cathode gridhaving a row array of apertures each aligned with the verticalintersection of one of the scan anode and cathode elements andcommunicating with the cathode grid electrode elements through at leastone of the openings in the cathode grid, and a display anode gridoverlying the apertured spacer, the display anode grid having paralleldisplay anode elements with each element aligned with a row of aperturesin the apertured spacer and with a scan anode electrode element, thedisplay anodes further comprising a low voltage cathodoluminescentphosphor.
 11. The display device of claim 10 in which the low voltagecathodoluminescent phosphor is P15 phosphor and the gas comprises neon.12. The display device of claim 10 in which the display anode gridelements are coated on the side facing the aperture array with aninsulating material and further have at least one opening through theregion of their thickness corresponding with each aperture to allowelectrons drawn from the aperture to strike the side of the displayanode elements that faces the insulating top plate.
 13. The displaydevice of claim 10 in which the gas comprises neon.
 14. The displaydevice of claim 10 in which the gas comprises xenon.